The Heart Thief
by zhec
Summary: Extracting the darkness from the boy's heart should have given birth to the two pure hearts of light and darkness needed to forge the key to the Next World. As half expected, the former began to drift toward eternal sleep, the remnants of the once whole heart slipping away like sand in an hourglass. The latter, however, retained a smudge of light. Cross-posted from AO3.
1. Nulla

Torn, slit, and punctured, they piled in mountains and plains that stretched across the void. They had no pulse or color. The newborn heart didn't know what fell its kind, nor did that matter now. What started as whimpers that reached the far corners of this realm twisted into wails billowing in the sea of the dead. Someone was hurting.

The little one hurried.

Over the strewn corpses peered a living heart. It was the one wailing. The reason became apparent.

"Stop!"

The other was all but cleaved in two, along the line that divided its light and darkness, milk white and tar black. A key-shaped blade protruded from its lower appendage, sawing through the dwindling number of filaments that kept the sagging halves attached.

"I said quit it!" The little one grasped the grip of the enchanted sword, heaved, and was yanked along. To the beat of cracks and rips, over the sizzle of the other heart's tears, the weapon with no mouth to and froed in the shape of a sneer, as if laughing. The little one wouldn't let go. It couldn't.

As if hearing their owner's wish and possessing a will of their own, strands of yellow seeped out of him unbidden and wove themselves into the halves. More filled the break, slowly mending the other heart. The little one swayed. It was giving its life away. It felt a tinge of regret from the burden it would become to its future soul and body, but there was nothing else it could do. The other heart needed it more.

So, when the sword tore through the bottom, pieces the little one had forfeited held the halves together.

The sword slashed upward, slicing through them.

One set of screams split into two.

"No!"

A tempest erupted in the rift between them. Visible winds surrounded the one of pure darkness as the eye of the storm. The gale swept through the little heart. It failed to save the two, and now it doomed its unknowing host to a life as a cripple for nothing. The little one choked. These thoughts weren't its own. There was so much contempt. It couldn't hold onto the weeping light half any longer and was swept away.

But there, inside the dark half, amid the swirling negativity was a speck of light—the little one's light. It couldn't save them, but maybe, that was enough.

* * *

 **Author's Notes**

Fair warning: I'm a very slow writer.

KH AU reboot where Sora's heart comes to the rescue earlier than in canon. He fails to heal Ventus's heart but manages to leave a bit of light inside Vanitas.


	2. I

His overhead strike stopped cold, in a clang of steel, on an immovable wall that was the flat of the master's blade, his two hands quivering against one that held firm no matter how hard he pushed. That wizened face showed not a tense, calculated look reserved for hostile threats but one of mere _disappointment_ for his act of defection. Vanitas snarled. Why, why was he, no longer held back by his pathetic Light, still _weak_?

A flick of the master's blade staggered him. He froze. A white glove, inches away from his neck. The hilt's texture of thick braided cables slipped out of his dominant hand, Void Gear clacking sandstone. The rugged ground vanished from his feet and reappeared under his back. The master pinned him. He couldn't breathe.

 _Master won't kill me._

Fingers clawed at the gloved hand.

 _He needs me._

Black spots. They weren't Heartless.

"—blade Graveyard—fitting—suppose—"

Air.

He burst into coughs. With a scuffle of feet, the master disappeared.

Something black darted by. Vanitas seized his new keyblade, snapping his head toward the direction it ran. Dark shapes were hounding the blurred image of the master. Heartless? He whirled around. No one else was there, only the blond weakling on the ground. Those shadowy things around the master didn't seem to have the yellow eyes.

And they seemed only interested in harming the old man.

Vanitas scrambled to his Light. The other blonde lay stiller than a wind-up toy with a broken mainspring, glazed blue eyes lost in the sky smothered in murky red. The wails, the writhing, they had stopped.

He could 'hear' a faint heartbeat.

"H-hey!" His voice came out hoarse. "Get up!"

A crack rang, the very one that ripped through their original self's heart when the master tore it in half.

"Don't die on me, idiot!"

There was no whisper, no twitch in the body, but thundering palpitations from a mangled heart he could 'see' inside the weakling. It spasmed and stopped, spasmed and cracked.

"Damn it!" He hurled his keyblade. It clattered and vanished into thin air, sheathed in the recess of his conscious. He needed to calm down. They had to get away, to another world. It didn't matter which. Anywhere else. He lifted the other blonde, stumbling under the unexpected weight. They had never opened an interstellar portal. The weakling never let him. Big load of 'good' that did them.

A shriek, an octave higher than their own, like that of a replicant of themselves being burned alive. He glanced over his shoulders. Barbed steel jutted out from the writhing flesh of one of those Heartless-like things. The monster sublimed from head to toe, black tendrils coalescing into a wisp of vapor. It rushed toward the two. Toward the weakling.

He spun. Too late—or not. It slithered around his other half, passed through the crannies of the helmet that their separation had granted him, and plunged into his mouth and down his throat.

 **xxx**

 _"Get up, boy." A white gloved hand lifted him by the head from the blood-smeared marble floor, past his height. His legs hung limp in the air, and gravity stretched his neck. He felt fingers squeezing his skull. 'Stop' reached his split lips but ended there. Through the training hall, a crunch resounded._

 **xxx**

A memory. He crumpled. It was supposed to be a memory. He twisted around and forced the crown of his head, where a thumb once was, against the helmet's liner. A screech drowned out all others. His.

 **xxx**

 _His jaw dropped. A weird giant key like his had flashed in the old stranger's hand with a glimmer. After one beckoning wave too, unlike his most of the time._

 _"The keyblade. Since ancient times, this power has been bequeathed from generations to generations, entrusted to wielders to bring and maintain balance between darkness and light. It seems fate has destined the two of us to meet, boy. You seek answers. I can see it in your eyes."_

 _Here was someone else like him, and more out there if the stranger wasn't lying. And if the other wasn't, if other habitable worlds really did exist, that could explain the stranger's getup. That could explain his own clothes too, the ones people still mocked to this day, and why no one knew him. He broke into a grin. Maybe, maybe this person could help._

 **xxx**

More wisps invaded him.

 **xxx**

 _Ravenous, glowing eyes stared into his no matter which way he turned. They crept toward him. More emerged. Clutched close to his chest, the keyblade shook in his sweaty palms. The master's footsteps grew faint, footsteps of the sole living constant in his life. "Please don't do this, Master! I'm not strong enough!"_

 **xxx**

And with them, memories. Too vivid, too real, as if they just happened. "Stop," he whimpered. "I didn't ask for this." The master was still there, an inescapable constant.

Underneath Vanitas, a cool fluid welled up, spilling over to the ground around him. It rose to the nape of his neck. He was being submerged, as if the fluid was devouring the layer of earth. Viscous tendrils snared his neck and limbs. He couldn't break free.

Rocky badlands and overcast skies vanished, swallowed by a boundless abyss devoid of light except his own joining his fall. Corridors of Darkness. He somehow opened one. Or the master was giving him false hope.

He squinted. In this pitch-black nothingness, his Light shone white. Too bright. Gritting his teeth, he grasped for the weakling. Why bother? Not like he knew how to become whole.

Not like his whole self chose listening to him over dying.

Behind the weakling, a shade of impure black cut through the monotony, undulating toward the dark half. He recognized it. A hiss escaped as he jerked his outstretched arm back.

It stabbed him in the chest.

 **xxx**

 _A streak of light flit through Aquarius's urn, which he just found. Another across Aquila's wings. Three beat the lowest recorded zenithal hourly rate. The number didn't stop. More rained, amid tens of constellations, thousands of stars, from the impossibly clear, moonless sky, breathing life into the dreary wasteland. A night more magical than any spell it was. He jumped up on the barren summit, shot a hand up into the air, and spun around—"Master!"_

 _The master wasn't there._

 _Heaviness weighed on his shoulders. Right._

 **xxx**

"You're," his voice did _not_ break, "really pathetic, you know that?"

No response besides more heartbeats.

Crack. And that.

One fragment. Two. Shivers of white splintered off that sickening mass of sunshine, as if they were solid, and faded, lost to the darkness. The light dimmed. Parroting the state of the outer body, the heart was crumbling. Perhaps the cause and effect were the other way around. Whatever, he should ignore them. Those good-for-nothing leftovers could rot for all he cared. Nobody wanted the whole loser anyway.

Another piece fell. He didn't need it.

He didn't.

With a trembling arm, he reached for the weakling once more. Sweat trickled along his jawline and seeped into the helmet's liner as he wove a spell. A red and a blue orbs materialized at opposite sides in orbit, slowly disintegrating into dust that spiraled to the center, him. From a feet away.

The weakling was several past that.

Their original could do better than this. Vanitas grunted, tempted to set the light-sided idiot on fire instead. He didn't.

Something was watching them from behind. He could sense it. Fidgety, waiting to pounce something, no, someone.

He tugged the intangible link that tied him to the orbs from himself. Panting, he tried again. Again. And again, each time pushing the spheres farther and widening their path of orbit.

They circled past the other blonde.

The light half fell faster, toward him. Bile crawled up his throat, a sign that he had been subjected to the center of the magnetism spell for too long. His muscles begged for mercy. He wouldn't stop. Not yet.

He needed to prove he was stronger than the original.

Seconds trudged by. Almost.

There. He grabbed the other by the wrist.

The crumbling stopped. The heart slowed to a steady beat.

* * *

 **Author's Notes**

In the Birth By Sleep game, our evil friend explains that whenever an Unversed is destroyed, its negativity flows back into him. The novel is more specific by having him feel pain. Here, he instead relives a memory (which may of course have him undergo pain) associated with the emotion that the creature represents. The Unversed in this chapter are centered around two feelings. I'll let you figure things out from there.


	3. II

**Author's Notes**

Added a plot detail about a presence Vanitas sensed in the corridor near the end of the previous chapter. Also fleshed out a couple memories in that chapter.

FFN unfortunately doesn't let me change the margins or align paragraphs to the right. As a result, I have to compromise on the formatting of some of the memories in this chapter. The AO3 version I posted under the same pen name and title is closer to the intended formatting, so feel free to check it out there if you're curious.

FFN also doesn't seem to let me skip lines, so you have to deal with every memory being separated by xxx's. This chapter has a lot.

* * *

The rush of wind and spreading hues of white and blue greeted the two halves at a new world. Formerly boundless, the vacuum receded to a swirling portal haloed by sunlight, shrinking into the distance. They were falling. From how high, Vanitas didn't know.

He tried to pull his other half in, his grunts as fierce as the roaring wind. The black swirl waned to a dark spot on a un-eclipsed sun, which didn't help matters.

Cobwebs of green leaves swallowed them up and drowned them in cascades of rustles and flaps. Twigs hardly slowed the pair down, handing out cuts and splinters as a half-baked apology. Something slammed onto his back. Hard. Something else crashed into him. The weakling. The weakling was on top of him. The dark half wrapped the other blonde in his arms. He could handle a broken back. He could handle jagged branches slashing his upper arms. Unlike his counterpart, he wasn't fragile.

With a jolt and a thud, everything went still.

And still.

Blood trickled down his helmet's visor. It wasn't his.

On him sprawled the weakling, littered with marks, blood pouring from the back of the head. Arms as stiff as clock hands, he fumbled the other's torn jacket again and again. Scowling, he shifted the dead weight to the left, where the wettest part of the other's head lay hugged between his chest and shoulder.

"You're," he wheezed, "welcome."

The weakling had stopped radiating light. It faded when they entered this world, probably elicited through places blessed with as much darkness as the corridor. Despite its disappearance, ever since he grabbed the other blonde, the other heart hadn't broken further. He could guess why but wasn't inclined to test that theory. Not because reclaiming what was once his meant that much but because he already spent, wasted, a great deal of effort keeping the loser alive.

The ground underneath grew sticky and wet. Overgrown blades of grass brushing against his side blackened—blackened? Ooze that resembled those spilled from slain Heartless puddled the once rich green. He traced a rivulet of the substance to a line of cleft fibers in his ribs.

It was blood, his blood. The gash exposed more fibers, some tinged with crimson, but no trace of human skin. This wasn't his body. Or a power suit.

So the name wasn't enough. The Light stole his body too.

Chirps descended into fleeing cries. The forest fell silent, permeated with labored and soft breaths. Something was watching him again, more of it this time. Their presence felt the same as the one from the interstellar corridor.

Wakes of rustling leaves broke the stillness. He followed them with his eyes. Monsters akin to the ones in the previous world hung under low boughs. Slit red eyes flickered between the two, lingering on, settling on the body thief.

A pair of zigzag ears twitched.

He held the thief tighter.

Tiny feet pattered on wood.

"Stay, away."

They didn't; they dove.

The blonde was in the way, like last time. Vanitas wanted to scream.

Black vapor swooped down. From it emerged an arm with a buckler, smashing the rodents into bark with a splat that would be music to his ears had he been the perpetrator. He didn't need to be saved by this, this fat abomination shoved into tacky knight armor. It marched toward his assailants, its back facing him, but he knew it was another red-eye. He felt a connection to it, one not much different from those to the flock. The latter were apparently how he detected the other red-eyes. In retrospect, similar connections were present when their brethren popped up in the badlands.

He swatted the growing implications.

The flock launched at the thing standing before it.

The shrieks returned. They weren't missed.

 **xxx**

 _Across the floorless corridor, the two trod as though an invisible plane lay suspended underneath, one that devoured footsteps. His cloak remained fastened, its cowl raised. The master never tried to rip it from him, keeping those white hands clasped behind the hunched back, but he kept several paces behind in case the master ever considered such a notion._

 _"You won't learn to control the darkness in you if you persist in wearing that here."_

 _"I'm not taking it off, Master." Not after the first time._

 **xxx**

His fingers dug into the thief.

 **xxx**

 _"These matters do not concern you." The master vanished with the portal. Again._

 **xxx**

 _Today marked 255 days since he woke up inside that abandoned mansion without any memories, 255 with not one resurfaced clue of where he came from or whom he met before, 118 since the master promised to help rediscover his past. The master 'helped' all right, if a vague link to a war that transpired centuries ago was all he needed to know. Since that speculation, that guy kept a tighter lip about where he went off to. Something was up._

 **xxx**

They always came to him. Always. Never the other who still dared wear the face of an apathetic bystander.

 **xxx**

 _"Why didn't you tell me there's another way to travel besides those corridors?!"_

 **xxx**

He caught gaseous tendrils squirming out of his, this, body and coagulating into familiar silhouettes.

The flock was winning.

 **xxx**

 _"You hardly ever take me to other worlds now! I'm sick and tired of being trapped in this godforsaken wasteland in the middle of nowhere with a load of dead—"_

 **xxx**

His body jolted. His left cheek stung. Yet, the pest didn't stir.

Around the rodents and the knight wannabes—there was another—more red-eye breeds warred. Rabbits, bats, shoes.

 **xxx**

 _Sallow eyeballs slid off the melting flesh around the master's blade. With a yelp, he started back, kicking up dust in his wake. A split second too late and a spatter of ooze would had landed on his feet. The eyes dissolved in the puddle like saliva-coated prey in gastric acid. Yet, the smell was tantalizing. It was a promise of respite, and all he needed to do was come closer. His gut screamed at him to flee; the master's presence held him on a leash._

 _"What you witnessed was the fate of those who allowed their hearts to be consumed by darkness. They devolved, from both mind and body, into empty creatures driven by the instinct to feast upon more hearts. The precepts have a name for them."_

 **xxx**

Vanitas grabbed the rotten existence by the throat.

 **xxx**

 _He shrunk away from the master's looming figure. "You wanted me to turn into one of them all this time. That's it, isn't it?"_

 _"Not become. Tame."_

 **xxx**

It felt like the grip of his keyblade, like thick braided cables. He knew better. Nothing was wrong with the neck or the grip. It was him. Him and these grotesque mimicries of human hands.

 **xxx**

 _"Empty creature from Ventus riven, to you the name Vanitas shall be given."_

 **xxx**

"You, little, _wretch!_ "

A deafening sledgehammer force joined a flash of light.

 **xxx**

 _"You see how powerless you are? Curse that frailty of yours. Let your heart blacken with rage!"_

 **xxx**

It threw him headfirst into a bole. His body burned as if peeled and then dragged against a gravel road. A familiar weight set on him. He snapped his eyes open, met with a scorched, infuriatingly blank face—his real one—pressed against the grimy front of his helmet, a discolored neck clenched in his torn hands.

He didn't let go.

Another flash of light came.

 **xxx**

 _"Yes, boy, that's it! More!"_

 **xxx**

A torrent of wind shoved the two against the bole. Branches collapsed on a den of colorless flames spreading alongside muffled cries. It hadn't reached here yet.

 **xxx**

 _He couldn't do it._

 **xxx**

 _Greeted with the taste of copper again._

 **xxx**

 _"Still so blind."_

 **xxx**

His arms gave out.

No, he could still—

 **xxx**

 _Maybe leaving that town and apprenticing under the master was a mistake—_

 **xxx**

 _He wondered how those three were doing—_

 **xxx**

 _—The master called him one anyway._

 **xxx**

 _—They probably wouldn't care about a missing nobody._

 **xxx**

—squeeze out of the leech.

 **xxx**

 _"Really?" You would rather die than use the power? Feckless neophyte."_

 **xxx**

Only his left arm was stuck. He—

 **xxx**

 _"—blade Graveyard—fitting—suppose—"_


End file.
